Use of the 1:2 chromium complex of 1-amino-2-(3&#39;, 5&#39;-dinitro-2&#39;-hydroxyphenylazo)-4-sulfonaphthalene and alkali metal salts thereof for dyeing polyamides and oxide layers on aluminum and aluminum alloys

ABSTRACT

Disclosed are the 1:2 chromium complex of the formula ##STR1## and the alkali metal salts thereof which are useful for the coloration of oxide layers produced on aluminum and alloys thereof and for dyeing natural and synthetic polyamides.

This application is a division of application Ser. No. 964,698, filedNov. 29, 1978 and now U.S. Pat. No. 4,416,816 issued Nov. 22, 1983,which is a continuation-in-part of application Ser. No. 373,630, filedJune 26, 1973 and now abandoned.

The present invention relates to anionic 1:1-chromium complexes, theirproduction and use as dyes.

The present invention provides the 1:2 chromium complex of formula I,##STR2## and the alkali metal salts thereof.

The present invention further provides a process for the production ofthe chromium complex of formula I characterized by treating a compoundof formula II, ##STR3## wherein Y is hydrogen, C₁₋₄ alkyl or acyl, witha chromium donor.

Suitable chromium donors include, for example, the chromic salts, suchas chromic fluoride, chromic chloride, chromic sulphate, chrome alum,chromium-ammonium sulphate, chromic formate and chromic acetate, andalso complex salts of the Cr⁺⁺⁺ ion, such as chromic oxalate, chromictartrate, chromic lactate, chromic salicylate, chromic oxide and chromichydroxide. Salts of hexavalent chromium, in which the chromium is in theanionic radical, such as potassium and sodium chromates and dichromates,are also suitable. In the latter case, it is preferred to carry out thechromatisation in an alkaline aqueous medium in the presence of areducing agent, such as furfural or glucose.

The quantity of the chromium donor is selected in such a way that atleast one atom of chromium is available for two molecules of the monoazocompound of formula II. In general, it is recommended to use less thantwo atoms of chromium per two molecules of the compound of formula II.

Chromatisation is preferably carried out in an organic solvent misciblewith water, such as formamide, glycerol or ethylene glycol, in water orin a mixture of the above solvents with water. It is recommended thatthe reaction be carried out at a pH greater than 4, i.e. under slightlyacid, neutral or alkaline conditions. The conversion of the monoazocompound to the chromium complex is preferably carried out at atemperature within the range of 80° to 135° C., or at the boiling pointof the reaction mixture, either under atmospheric or super atmosphericpressure. The reaction may be assisted by the addition of substancesfavourable to complex formation, such as oxalic and tartaric acids, orsubstances exerting an influence on the pH.

As will be appreciated, during complexing of compounds of formula IIwherein Y is C₁₋₄ alkyl or acyl, such groups are split off during thereaction.

It is also possible to carry out chromatisation in two stages, as inprocesses of the prior art, in that the compound of formula II istreated with a chromium donor in such a manner that the reaction productcontains one atom of chromium per molecule of this compound, after whichone molecule of this reaction product, i.e. a 1:1 chromium complex, ismade to react further with one molecule of the compound of formula II.

Separation of the final product is carried out in a conventional manner.For example, solutions of the product in organic solvents are dilutedwith water; the product itself may then be precipitated from the aqueoussolution by cooling, possibly with the addition of salts. After this,the product is separated by filtration, followed by drying and grindingto a powder, if desired.

The compound of formula II can be obtained by diazotising1-amino-2-hydroxy-3,5-dinitrobenzene, for example by means of sodiumnitrite and hydrochloric acid in an aqueous solution, followed bycoupling the resulting diazonium compound with1-aminonaphthalene-4-sulphonic acidic in a neutral or slightly acidmedium. Chromatisation of the compound of formula II by means of achromium donor may be carried out in the coupling mixture. However, forpractical reasons it is advisable to separate the compound of formula IIby means of filtration, if necessary after the addition of salt, andthen to treat the filter cake (without drying) with the chromium donor.It is also possible, however, to start with the compound of formula IIin dried form or after purification by recrystallisation.

By the term "acyl" as used herein is understood the residue whichresults from removing a hydroxyl group from an acid or hypothetical acidand is understood to include radicals of the formulae

    R--O--CO--, R--SO.sub.2 --, R--O--SO.sub.2 --, R'--NR'--SO.sub.2 --, R'--NR'--CO--, R'--CO--

and wherein

R is an alkyl radical of 1 to 4 carbon atoms or a phenyl radical, and

R' is hydrogen, an alkyl radical of 1 to 4 carbon atoms or a phenylradical.

The complexes of formula I are readily soluble in polar solvents such asethylene glycol and formamide, and particularly in water, and aresuitable for dyeing or printing various materials, such as natural andsynthetic polyamides, for example wool, nylon and leather. The complexesof formula I are also particularly suitable for dyeing artificiallyproduced oxide layers on the surface of metallic aluminum, i.e. layersproduced by chemical or preferably anodising processes, preferably inaqueous solutions. Oxide layers dyed with a complex of formula I arecharacterized by good resistance to fading and particularly by thequality of their neutral grey colour.

By oxide layers produced by anodising processes is meant porous layersof aluminum oxide adhering firmly to the base metal, such as thoseproduced by electrochemical treatment of the aluminum surface in anelectrolyte containing water and a suitable acid, using direct currentwith the aluminum workpiece forming the anode. By the expression"neutral grey colour" is meant anthracite greys of the kind producednaturally by the anodising process described in more detail below.

In the field of surface treatments for aluminum, coloured oxide layersproduced by anodisation play an important part owing to theirexceptional resistance to mechanical damage and corrosion and also theirhighly decorative effects. In order to produce coloured oxide layers ofthe type defined, several basically distinct processes are available.

In a single-stage process, known as anodisation with self-coloration("Integral Color Anodizing" or "Anodisation autocolorante") specialaluminum alloys are used, and generally special organic acids as theelectrolyte. Such processes are characterized in that the oxide layer isformed and coloured at the same time during the anodising process,whereby the colour is produced by the chemical or physical conversionand deposition of alloy constituents in the aluminum oxide layer.Consequently, the colour is generally dependent on the composition ofthe aluminum alloy used as a base.

In a two-stage process, a preferably colourless and transparent oxidelayer is first produced by anodisation. Subsequently, colouring matteris introduced into the pores in the oxide layer, a distinction beingdrawn between electrolytic and adsorbtive deposition of the saidcolouring matter.

In the first case, namely that of coloration by the electrolyticdeposition of metallic salts, the anodised aluminum is immersed in anaqueous solution which, in addition to an acid, contains special saltsof heavy metals such as nickel and copper, the said metallic salts beingdeposited and converted by the passage of an alternating current in theform of coloured metals or metallic compounds.

In the second case, namely that of coloration by adsorption, theanodised aluminum is treated with a solution preferably containing anorganic dyestuff. Aqueous solutions of anionic dyestuffs have been foundto be particularly suitable for this purpose. In this case, colorationoccurs by a purely adsorbtive process without the use of an electriccurrent.

Adsorbtive coloration processes are superior to electrolytic processesin several respects. Since the coloration is on the one hand independentof the composition and state of the alloy and on the other of anelectric current, the adsorbtive process requires less storage space,apparatus and supervision. Also, the slight differences in alloy qualityand current distribution which are unavoidable in practice can have noadverse effect. Coloration produced by the adsorbtive process is hencecharacterized by a greater degree of evenness and reproducibility. Owingto its simplicity, adsorbtive coloration is unrivalled from the economicpoint of view.

However, it is sometimes necessary to use the electrolytic colorationprocess since certain preferred colours cannot be produced in asatisfactory way by the adsorbtive method. For example, it is necessaryto produce the particularly valuable neutral grey tones by means of aspecial form of the anodising process with integral coloration. Theprocess known as anodising with integral grey coloration comprisesanodising aluminum alloys with a silicon content exceeding thesolubility limit, for example 3.5 to 8% silicon, in dilute sulphuricacid. The production of such alloys with uniform quality and theiranodising involve particularly great difficulties, which have an adverseeffect on both the economy of the method and the uniformity of the greycoloration produced.

In view of the above-mentioned drawbacks of this method, attempts havebeen made for a long time to find a way of producing neutral grey tonesby adsorbtive means, although no satisfactory solution has been found inthe prior art. It was in fact found possible to produce neutral greytones by the simultaneous use of several organic dyestuffs. However,when organic dyestuffs are used, it is necessary on economic grounds touse the same bath for a prolonged period, which involves drawbacks whichare very difficult to overcome when mixtures of different dyestuffs arebeing used. The different rates of impoverishment in the various colourcomponents causes unwanted variations in the tone of the coloration,which are particularly noticeable with neutral grey colours. Deviationsfrom the original colour tone cannot be very satisfactorily corrected bysubsequent additions to the dyeing bath.

It has now been discovered quite unexpectedly that it is possible tocolour artificially produced oxide layers on aluminum evenly in neutralgrey tones ranging from light to very dark by treating the said oxidelayers on aluminum with a solution of a complex of formula I.

The treatment occurs in accordance with methods known in the prior art.For example, a complex of formula I dissolved in water, an organicsolvent such as a C₁₋₄ alcohol, acetone, ethylene glycol or a mixturethereof, may be applied to the anodised aluminum by means of brushing,swabbing, etc., or by spraying.

Also, for the purposes of graphical reproduction, the solution of acomplex of formula I may be converted into a printable form by theaddition of a viscosity improver and applied to the oxide layer by agenerally used printing process, for example with a rubber stamp or by asilk-screen process. The best method, however, is by immersion of theanodised aluminum in an aqueous solution of a complex of formula I. Bysuitable masking of the oxidised surface layer it is possible with theimmersion method to obtain partial and varied colour tones. Thetreatment may be carried out at normal temperatures, i.e. over the rangebetween ambient temperature, e.g. about 25° C., and the boiling point.Temperatures between 55° and 65° C. are particularly favourable. The pHis so chosen that the oxide layer is either not attacked or onlyslightly attacked, i.e. dyeing is preferably carried out in the pH rangeof 4.5 to 6. Adjustment and maintenance of the pH may be achieved by theuse of the usual acids and bases, such as sulphuric acid, acetic acidand sodium hydroxide solution. If required, other additives generallyused to improve the coloration process, such as equalising additives,buffer reagents and organic solvents miscible with water may be used.

The dyestuff concentration and time of treatment may be varied over awide range, according, among other things, to the required intensity ofthe grey tone, the thickness and structure of the oxide layer, as wellas the other dyeing conditions. The preferred concentration range isfrom 0.01 to 10 grams/liter, more preferably 0.1 to 10 grams/liter. Thepreferred treatment time is from 1 to 30 minutes. A treatment time of 15to 20 minutes is particularly suitable.

By aluminum is meant not only pure aluminum, but also those aluminumalloys which behave in a similar manner to the pure metal with regard toanodic oxidation, such as alloys of the type Al/Mg, Al/Si, Al/Mg/Si,Al/Zn/Mg, Al/Cu/Mg and Al/Zn/Mg/Cu. As electrolytes for the anodisingprocess, chromic, oxalic and sulphuric acids can be used, among others,as well as mixtures of oxalic and sulphuric acids. Particularly valuableresults can be obtained by the use of alloys and anodising processeswhich result in transparent, colourless oxide layers. The direct currentsulphuric acid process has been found to be the most suitable anodisingmethod. However, it is also possible to use alloys and anodisingprocesses which produce integrally coloured oxide layers.

The process may also be carried out in such a manner that dyeing occursat the same time as the anodic production of the oxide layer or so thatthe complex of formula I is actually produced in the dyeing bath.

The complexes of formula I are also suitable for the coloration ofchemically produced oxide layers on aluminum, the so-called conversionlayers as produced, for example, by the effect of baths containing thesalts of chromic acid in acid or alkaline media.

After dyeing, the coloured oxide layer is processed in the usual manner.A particularly advantageous method is the sealing of the oxide layer bytreatment with boiling water or steam, if necessary in the presence of areagent which aids sealing and at the same time inhibits leaching out ofthe dyestuff, such as nickel or cobalt acetate.

In view of the large number of organic dyestuffs suitable for thecoloration of anodised aluminum known in the prior art, it could in noway be foreseen that the complexes of formula I would enable neutralgrey tones to be produced by the adsorptive method for the first time.This result is all the more surprising in view of the fact that the useof closely related chemical substances does not produce a greycoloration. For example, the use of the chromium complex of the monoazodyestuff obtained from diazotized 1-amino-2-hydroxy-3,5-dinitrobenzeneand 1-aminonaphthalene-5-sulphonic acid gives olive-green tones. If thechromium atom combined as a complex in the dyestuff of formula I isreplaced by a cobalt atom, a black colour is produced on anodisedaluminum, in accordance with Example 1 of Swiss Pat. No. 363,744. If thecobalt complex is used in low concentrations, olive-green tones are alsoproduced. Neither are grey tones obtained with any of the otherdyestuffs described in the said patent. If the chromium complex of themonoazo dyestuff obtained from diazotized1-amino-2-hydroxy-3,5-dinitrobenzene and 1-aminonaphthalene-4-sulphonicacid, in which one chromium atom is combined as a complex with onemolecule of the monoazo dyestuff, giving a 1:1 chromium complex, agrey-blue coloration is produced.

It will be appreciated that the complex of formula I may be used inalkali metal salt form, especially the sodium salt form.

The following Examples serve to further illustrate the invention. In theExamples all parts and percentages are by weight and the temperaturesare given in degrees centigrade unless otherwise stated.

EXAMPLE 1

43.3 Parts of the monoazo dyestuff obtained from diazotized1-amino-2-hydroxy-3,5-dinitrobenzene and 1-aminonaphthalene-4-sulphonicacid, 39 parts of an aqueous solution of chromium acetate containing11.8% Cr₂ O₃ and 400 parts of water are refluxed with stirring for 10hours. During the reaction the pH of the chrome-complexing mixture ismaintained at 5.0 by means of aqueous sodium hydroxide solution. Aftercooling to room temperature, the crystallized reaction product isseparated by filtration, dried and powdered. In pure form, the 1:2chrmium complex of the monoazo dyestuff is obtained as a dark-greypowder, soluble in sulphuric acid to give a blue-red solution and inwater to give a grey solution. The dyestuff colours anodically oxidizedaluminum to give a neutral gray tone particularly resistant to fading onexposure to light.

Alternatively, if instead of drying the product obtained afterfiltration, the filtercake is dissolved at room temperature in a mixtureof 19 parts of crystalline sodium acetate, 27 parts water and 111 partsdiethylene glycol monoethyl ether, 230 parts of a stable liquid,homogeneous dark grey dyestuff preparation are obtained. Suchpreparation does not crysallize after prolonged storage at 0° C. andgives a clear solution in a matter of seconds when added to water.

The liquid preparation gives dyeings on anodically oxidized aluminumwhich have the same properties as dyeings made with the pure dyestuff.

The chromium complex may also be obtained by reacting 48.3 parts of the1:1 chromium complex of the compound of the formula ##STR4## with anaqueous solution containing 43.3 parts of the monoazo dyestuff usedabove in 1000 parts of water at 70° C. and pH 4.8.

EXAMPLE 2

43.3 Parts of the monoazo dyestuff used in Example 1 are dissolved in1000 parts of water at a pH of 8 to 9. The resulting solution ismaintained at 100° C. for 1 hour, during which time 200 parts of anaqueous solution containing 8 parts of potassium dichromate and 18 partsof glucose is added dropwise. At the end of the reaction period, thechromium complex is precipitated by the addition of sodium chloride,separated and dried. The resulting substance is the chromium complex ofthe dyestuff described in Example 1.

APPLICATION EXAMPLE A

A degreased and stripped workpiece of pure aluminum is anodicallyoxidized for 30 minutes at a temperature of 18° to 20° C. with a directcurrent of density 1.5 amperes/dm² in an aqueous solution containing 20parts of sulphuric acid and 1 part of aluminum sulphate per 100 parts.

After rinsing with water, the workpiece is immersed for a period of 15minutes at a temperature of 60° C. in a solution containing 0.3 parts ofthe chromium complex produced in accordance with Example 1 in 1000 partsof deionised water whose pH is adjusted to 5 by means of acetic acid.The dyed workpiece is rinsed with water and then treated for 30 minutesat a temperature of 98° to 100° C. with deionised water. The result is amedium neutral grey coloration with a good resistance to fading onexposure to light.

If the said aluminum workpiece is printed prior to dyeing with alinseed-oil based printing ink by the offset process, and cleaned withxylene after the treatment with boiling water, a natural-colouredpattern on a grey background will be obtained.

If the workpiece is oxidised under otherwise identical conditions for aperiod of 60 minutes and then dyed in a solution containing 10 parts ofthe chromium complex per 1000 parts of water, a deep grey coloration ofoutstanding resistance to fading on exposure to light and weatherconditions is obtained.

If the after-treatment is carried out under otherwise identicalconditions with a buffered solution of the complex containing 3 partsnickel acetate in 1000 parts of water, a coloration of the same qualityis obtained.

APPLICATION EXAMPLE B

10 Parts of the complex produced according to Example 1 are dissolved in500 parts of water and stirred to form a highly viscous mixture with asolution comprising 400 parts of water and 100 parts of methylcelluloseof a medium degree of polymerisation and 1.5 degrees substitution. Theprinting ink so obtained is applied by a silk-screen process to a dryoxidised aluminum sheet obtained by anodising an aluminum alloy of thetype Al/Mg/Si(0.5) for 30 minutes in a solution of 100 parts chromicanhydride in 1000 parts of water at 53° C. and a current density of 1.2amperes/dm². The printed aluminum alloy sheet is immersed in boilingwater for 10 minutes and then rinsed throughly in cold water. A greypattern on a pale greyish background is obtained.

What is claimed is:
 1. A process for the coloration of a porous oxidelayer on an aluminum or aluminum alloy substrate comprising contactingan aluminum or aluminum alloy substrate having a porous oxide layerthereon with a solution of a dye, said dye being the complex of theformula ##STR5## or an alkali metal salt thereof.
 2. A process accordingto claim 1 wherein the solution is a solution of the dye in water, analcohol having 1 to 4 carbon atoms, acetone or ethylene glycol, or amixture thereof.
 3. A process according to claim 2 wherein the solutionis applied to the substrate to be colored by brushing, swabbing,spraying or printing or wherein the substrate is immersed in thesolution.
 4. A process according to claim 3 wherein the substrate isimmersed in the solution.
 5. A process according to claim 4 wherein thetemperature of the solution is about 25° C. to the boiling pointthereof.
 6. A process according to claim 5 wherein the temperature ofthe solution is 55° C. to 65° C.
 7. A process according to claim 4wherein the substrate is immersed in the solution for 1 to 30 minutes.8. A process according to claim 7 wherein the substrate is immersed inthe solution for 15 to 20 minutes.
 9. A process according to claim 4comprising immersing an aluminum or aluminum alloy substrate having aporous oxide layer thereon in a solution of a dye in water, an alcoholhaving 1 to 4 carbon atoms, acetone or ethylene glycol, or a mixturethereof, for 1 to 30 minutes, said solution having a dye concentrationof 0.1 to 10 grams per liter, a temperature of about 25° C. to theboiling point thereof and a pH of 4.5 to 6, said dye being the complexof the formula ##STR6## or an alkali metal salt thereof.
 10. A processaccording to claim 9 wherein the dye is a sodium salt of the complex ofthe formula ##STR7##
 11. A process according to claim 1 wherein the pHof the solution is 4.5 to
 6. 12. A process according to claim 1 whereinthe dye concentration of the solution is 0.01 to 10 grams per liter. 13.A process according to claim 1 wherein the substrate is aluminum or analuminum/magnesium, aluminum/silicon, aluminum/magnesium/silicon,aluminum/zinc/magnesium, aluminum/copper/magnesium oraluminum/zinc/magnesium/copper alloy.
 14. A process according to claim 1wherein the porous oxide layer on the substrate is an anodized oxidelayer.
 15. A process according to claim 1 wherein the dye is a sodiumsalt of the complex of the formula ##STR8##
 16. A process for dyeing anatural or synthetic polyamide substrate comprising treating a naturalor synthetic polyamide substrate with a dye, said dye being the complexof the formula ##STR9## or an alkali metal salt thereof.
 17. A processaccording to claim 16 wherein the dye is a sodium salt of the complex ofthe formula ##STR10##